
#include <iostream>

using namespace std;

int swap(int &a,int &b){
    int t = a;
    a = b;
    b = t;
}

int main(){

    int a=10;
    int b=20;
    cout << a << " " << b << endl;
    swap(a,b);
    cout << a << " " << b << endl;
    return 0;
}